NCAFM2023 Programme Booklet

Thursday 1440 - 1500

HIGH RESOLUTION AND IN SITU STRUCTURAL ANALYSIS OF ALLOY CRYSTAL SURFACES IN MOLTEN METAL BY VARIABLE TEMPERATURE AFM

Takashi Ichii* ,Yousuke Abe, Toru Utsunomiya, Hiroyuki Sugimura

Department of Materials Science and Engineering, Kyoto University, 606-8501 Japan Email: ichii.takashi.2m@kyoto-u.ac.jp

At the molten and solid metal interfaces, their alloy crystals are formed and grow. Since the size, shape, and geometric arrangement of the crystal grains heavily affect the macroscopic mechanical and electrical properties of metallic materials, in-situ analysis of the interfacial phenomena is significantly important. While AFM is powerful for high-spatial-resolution structural analysis of solid-liquid interfaces, the opacity of molten metal prevents the use of AFM with a Si cantilever and the optical beam deflection technique. Recently, we overcame this issue by using a qPlus sensor and achieved atomic-scale structural analysis on interfaces between molten gallium and Au-Ga alloy at room temperature [1]. The interfacial structures change with temperature, leading to differences in the type and thickness of the formed phases. Thus, in-situ observation of the dynamic processes under variable temperatures is of crucial importance. Here we report in-situ AFM observation of alloy crystals formed at the interface between molten Ga and Au-Ga alloy. Figures 1 (a)–(f) show temperature-dependent topographic images of Au-Ga alloy in molten Ga. At room temperature (Fig. 1(a)), faceted surfaces were imaged, which agrees well with our previous report. As the temperature increased (Fig. 1(b)-(f)), the facet surfaces disappeared from the corners of the crystal grains, and the grains changed to a rounded shape. This phenomenon is known as the roughening transition. After the temperature dropped again to room temperature (Fig. 1(f)), the grain shape became angular again, which is known as the facet transition. The transition temperature depends on the grain size, and we found a faceted grain even at 60 °C (Fig. 2(a)). On a facet of the grain, we achieved atomic-resolution imaging during layer-by-layer crystal growth (Fig. 2(b)), and found that AuGa 2 (111) surface was exposed. Thus, more insight into the crystal growth process in molten metal can be obtained with variable-temperature AFM.

References [1] T.Ichii, M. Murata, T. Utsunomiya, H. Sugimura, J. Phys. Chem. C, 2021, 125 , 26201.

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